In the wake of the slaughters this summer at a Colorado movie theater and a Sikh temple in Wisconsin, we set out to track mass shootings in the United States over the last 30 years. We identified and analyzed 62 of them, and one striking pattern in the data is this: In not a single case was the killing stopped by a civilian using a gun.

For the purposes of their study, they identified mass shootings as incidents in which four or more people were killed. Right off the bat, this suggests their conclusion is somewhat fallacious. The whole point is that the presence of other armed people on the scene might stop mass shootings from becoming mass shootings. Anyway, I cited a random sampling of examples where exactly that happened. A number of those incidents involved off-duty cops and I acknowledged this explicitly, while making the distinction that Mother Jones's definition of "civilian" seems odd and slippery:

Their claim that "not a single case was the killing stopped by a civilian using a gun" also raises a host of issues being that it is a conditional claim. Notice the word "civilian"? It's true that mass shootings are often stopped by police. But is that because they are uniquely qualified to stop mass shootings or that they stop killers simply by virtue of the fact that they are generally the first people to arrive on the scene carrying guns? ... I suppose the assumption that cops are better equipped to carry guns than civilians hinges on the fact that they are trained to handle guns. But so are military veterans, and there are millions of them who have likely as much or more firearms training as the average cop. Finally, it's also true that there are many people who have never had any law enforcement and military training yet are skilled and responsible firearms owners who are temperamentally well-suited to handle potential threats. Mother Jones makes no serious argument that arming more civilians wouldn't effective in preventing mass shootings.

The author of the Mother Jones piece responded to me on Twitter saying they had reported on the examples of armed civilians stopping shootings from escalating and they were "bogus." Let's take a look at some of the examples in this Mother Jones piece, "Do Armed Civilians Stop Mass Shooters? Actually, No.":

High school shooting in Pearl, MississippiAnother case, from 1997, in which the shooting was apparently already over: After killing two and wounding seven inside Pearl High School, the 16-year-old perpetrator left the building and went outside near the parking lot. The assistant principal—who was also a member of the Army Reserve—ran out to his own vehicle, grabbed a handgun he kept there, and then approached the shooter, subduing him at gunpoint until authorities arrived.

The Army Reserve's recruitment website encourages you to "discover what it's really like to be a civilian and a Soldier," pretty much underscoring my point that Mother Jones is being slippery here. Further, how does Mother Jones know the shooting was "apparently over"? The killer was stopped trying to drive away, and he was said to have been on his way to a nearby junior high school. Moving on: